1. Field of the Invention
The present invention relates to a method for recording with a magneto-optical recording medium. More particularly, the invention relates to a method and apparatus for recording with a magneto-optical recording medium, wherein the recording medium includes a recording layer and a reproducing layer for recording magnetic domains within the recording layer upon recordation and transfer of the record domains to the reproducing layer upon reproduction.
2. Description of the Prior Arts
The magneto-optical recording mediums and recording/reproducing apparatuses of this kind are disclosed, for example, in Japanese Patent Laying-open No. H6-295479 (Oct. 21, 1994) G11B 11/10, Japanese Patent Laying-open No. H8-7350 (Jan. 12, 1996) G11B 11/10, and so on.
The magneto-optical recording medium 10 includes, as shown in FIG. 1, a recording layer 14 and a reproducing layer 16 that are formed by a magnetic layer on a substrate 12. An intermediate layer 18 is formed between the recording layer 14 and the reproducing layer 16, while a protection layer 20 is provided on the recording layer 14. The intermediate layer 18, although formed herein by a non-magnetic layer, may be formed by a magnetic layer. Meanwhile, the recording layer 14 and the reproducing layer 16 may be formed by an arbitrary known magnetic material. Referring to FIG. 2, microscopic domains 22 can be recorded within the recording layer 14 of the magneto-optical recording medium 10 by using a magnetic head (not shown). During reproduction, the record domain 22 is transferred from the recording layer 14 to the reproducing layer 16 by irradiation of a laser beam 24 as shown in FIG. 3.
More specifically, a temperature profile is given in the magneto-optical recording medium 10 by irradiating the laser beam 24 as shown in FIG. 3. The temperature is highest at around a spot center and gradually decreases as an outer side is approached. Note that, in the case where the magneto-optical recording medium is for example a disc, the temperature profile is different in slant at between the front side and the rear side with respect to a moving direction of the magneto-optical recording medium. The temperature gradient is more abrupt at a region of the disc coming into a laser spot than that of a region going out of the laser spot. The magneto-optical recording medium 10 is increased in temperature at a desired point by utilizing such a temperature profile.
Returning to FIG. 2(A), if a laser beam 24 is irradiated to the magneto-optical recording medium 10, the magneto-optical recording medium 10 is increased in temperature to provide such a temperature profile as shown in FIG. 3. Here, the reproducing layer 16 is formed by a magnetic layer which is rich in transition metal and assumes a form of a magnetic thin film with perpendicular magnetization within a range from the room temperature to the Curie temperature Tc. As a consequence, the reproducing layer 16, if irradiated by a laser beam 24, is raised in temperature and decreased in coercive force. Due to this, the irradiation of the laser beam 24 causes the reproducing layer 16 to rise in temperature and hence decrease in coercive force, so that the record magnetic domain 22 of the recording layer 14 is transferred through the intermediate layer 16 to the reproducing layer 16 by the action of static magnetic coupling, thus forming a transferred magnetic domain 26 within the reproducing layer 16. The transferred magnetic domain 26 is formed at a position corresponding to the record magnetic domain 22.
After forming the transferred magnetic domain 26 within the reproducing layer 16, an external magnetic field Hep is applied by a not-shown magnetic head as shown in FIG. 2(B). This external magnetic field Hep is an alternating magnetic field. At least one period, preferably 2 to 4 periods, of an alternating magnetic field is applied during each time period that one magnetic domain passes through a hot spot 24a (see FIG. 3) caused by the laser beam 24. If an alternating magnetic field or external magnetic field Hep is applied in the same direction (same polarity) as that of the transferred magnetic domain 26, then the transferred magnetic domain 26 is increased in diameter to have enlarged magnetic domains 26a and 26b. As a result, transfer of the record magnetic domain 22 is effected with magnification. If a laser beam for reproduction is irradiated to the transferred magnetic domain 26 as well as to the enlarged magnetic domains 26a, 26b by using the optical head (not shown), reproduction is made of a magnetization state or record signals from the reproducing layer 16.
There is known one approach to realize high density recording, in the magneto-optical recording medium and recording/reproducing apparatus of this kind, wherein record magnetic domains are provided different in domain length 1T, 2T, 3T, . . . , as shown in FIG. 4.
In this conventional recording method, however, there encounters variation in a state of a leakage magnetic field passing through the reproducing layer of the magneto-optical recording medium due to difference in domain length. Thus there has been a problem that the optimal reproducing condition is different for each domain length thus resulting in worsened reproducibility.
More specifically, if considering a long domain as shown in FIG. 5(B), the reproducing layer has a leakage magnetic field that is strong at a domain end P1 but weak at a domain central region P2. Meanwhile, through an outside point P3 of the domain is caused a leakage magnetic field in a direction opposite to that of the domain end P1. In such a state, if an external alternating magnetic field be applied, the leakage magnetic field at the domain outer point P3 acts to prevent the magnetic domain from being transferred into and enlarged within the reproducing layer to a satisfactory extent.
On the other hand, where the domain is excessively short as shown in FIG. 5(A), the leakage magnetic field is less distributed throughout the domain. There is also reduction in the opposite directional leakage magnetic field at the domain outer side area. Accordingly, the application of an external alternating magnetic field causes the magnetic domain to be transferred to and enlarged in the reproducing layer with sufficiency.
It is therefore difficult, for the conventional high-density recording method to record by varying the domain length, to obtain a reproduction characteristic with uniformity, because of uneven transfer and enlargement of the magnetic domains into and within the reproducing layer due to the difference in domain length.
It is therefore a primary object of the present invention to provide a method and apparatus for recording with the magneto-optical recording medium.
It is another object of the present invention to provide a method and apparatus for recording with a magneto-optical recording medium which can stably reproduce under a same condition signals having been recorded by changing the domain length.
The present invention is a method for recording with a magneto-optical recording medium having a recording layer and a reproducing layer formed as a layer on a substrate, comprising the step of: recording a signal onto one part of a unit domain length (1T).
An apparatus for recording a signal on a magneto-optical recording medium according to the present invention, comprising: a modulating means for modulating a record signal; a timing signal creating means for creating a first timing signal based on the record signal modulated by the modulating means; and a magnetic field applying means for applying one period of an alternating magnetic field to a unit domain length in response to the first timing signal.
The physical length for recording a unit bit is taken as a unit domain length. In the case that the unit domain length is 1T, a signal xe2x80x9c1xe2x80x9d is recorded, for example, in 1T/2. More specifically, one period of an alternating magnetic field is applied to the magneto-optical recording medium during a time period of the unit domain length 1T. Accordingly, recording a signal xe2x80x9c1xe2x80x9d of 1T requires to record xe2x80x9c1xe2x80x9d in the former 1T/2 and xe2x80x9c0xe2x80x9d in the latter 1T/2. Recording a signal xe2x80x9c0xe2x80x9d of 1T requires to record xe2x80x9c0xe2x80x9d in both the former 1T/2 and the latter 1T/2. To record a signal xe2x80x9c1xe2x80x9d of 2T requires recording twice xe2x80x9c1xe2x80x9d and xe2x80x9c0xe2x80x9d alternately at a 1T/2 interval.
Because the substantial domain length is limited to 1T/2, the reproducing condition may be optimized only for the domain length of 1T/2. Also, there is less distribution of a leakage magnetic field through the domain, and there is reduction in an opposite directional leakage magnetic field that is formed at the outer side of the domain. Accordingly, it is possible to transfer and enlarge the magnetic domain to and within the reproducing layer in a sufficient extent.
According to the present invention, because the substantial domain length is taken short, even if the domain length is varied, the transfer and enlargement of the domain to and within the reproducing layer is made with sufficiency, thus realizing stable reproduction. Because the domain length is limited to one kind, it is possible to widen a margin for the reproducing condition.
The above described objects and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.